The invention relates to improvements in self-cleaning apparatus for dust filters comprising a plurality of porous fabric filter bags radially spaced in a cylindrical baghouse. The baghouse includes a sheet metal housing divided into two chambers referred to as plenums, by a tube sheet which support the plurality of vertically arranged bags. A dust-laden flow of air is introduced by fan into the dirty air plenum where the dust accumulates on the surface of the bags as the air passes through the bag fabric to the clean air plenum. Continuous filtration causes a cake of dust to build on the bags which unless removed will eventually block in air flow through the filter.
During the filtering operation, each of the bags is periodically back-washed by the application of a burst of clean air in the reverse direction through the bag to cause the accumulated dust particles and solids to be dislodged from the bag surface. The dust cake then falls to the cone shaped bottom of the dirty air plenum for subsequent removal. While there are numerous types of filtering systems on the market including wet scrubbers, cyclonic or electric precepitators; the preferred type is fabric filtration since it provides higher collection efficiencies and a relatively easy means for cleaning the filter medium.
Bag filters with various reverse flow air cleaning systems have been utilized in the marketplace for many years. The concept of a rotating sweeping arm, which back flushes individual filter bags has likewise been available for some time as exemplified by the patent to Caplan, U.S. Pat. No. 3,487,609 and the patent to Noland, U.S. Pat. No. 4,233,041. Most bag filters on the market utilize low pressure (3 to 5 PSI) air for the backwashing cycle such as the above-mentioned patent to Noland. However, distinct advantages have been discovered with the usage of high pressure air for the backwash circuit as exemplified in the patents to Pausch, U.S. Pat. No. 3,798,878, Borst, U.S. Pat. No. 4,247,310 and Caplan, U.S. Pat. No. 3,487,609. The last-mentioned reference to Caplan teaches a system that utilizes both low pressure reverse flow air in the cleaning cycle along with a high pressure blast creating a momentary shock wave in the bag. The patent to Borst generally teaches the concept of a high pressure jet which entrains outside air. The patent to Pausch teaches the concept of utilizing a venturi in conjunction with a high pressure blast to increase the amount of entrained air drawn into the bag in conjunction with the high velocity stream. However, this last-mentioned patent has a distinct drawback from the design of the present invention, in that substantial back pressure is always present on each of the bags in the filtering cycle by reason of the restricted flow path through the fixed venturis at the end of each bag.
The present invention has rectified this back pressure problem which severely limits the filter's capacity by providing a single moving venturi which momentarily passes over a filter bag and while blocking the normal filtering flow through the bag, inflating the bag with a sudden blow through the bag, inflating the bag with a sudden blast of compressed air. The partially collapsed bag over the cage momentarily expands to its maximum size causing the layer of dust cake adhering to the external surface of the bag to be released and dropped to the bottom of the baghouse for removal.
The main problem with low pressure filters, such as Noland mentioned above, is that the cleaning air is compressed only a slight amount and consequently there is very little shock effect by the reverse flow air through the bag and therefore the amount of dust removed is nowhere near that achieved with a blast of high pressure air.
With the use of a venturi, applicant has obtained an optimum utilization of this high velocity stream by entraining the stationary air surrounding the stream and drawing it through the venturi into the interior of the bag. At the same time the bag opening is otherwise covered by the closure plate so as to retain the air within the bag to maximize the shock effect. The utilization of a venturi in conjunction with a high velocity jet substantially increases the amount of air transmitted into the bag over prior art systems without a venturi. The present invention thereby obtains the same degree of cleaning at a reduced energy cost.
It is therefore the principal object of the present invention to provide a new and improved rotating arm high pressure cleaning system which utilizes a movable venturi in conjunction with the rotating arm.
Another object of the present invention is to provide a rotating arm cleaning system which is mechanically sequenced and operated.
A further object of the present invention is to provide an efficient rotating arm cleaning system which operates on high pressure plant air.
These and other objects and advantages of the invention will be apparent to those skilled in the art, after a consideration of the following detailed description, taken in conjunction with the accompanying drawings in which the preferred form of this invention is illustrated.